KVM: SEV: Do cache maintenance on the source VM during intra-host migrationgrafted

Manually perform cache maintenance on the source VM during intra-host
migration to ensure no stale data is left in CPU caches after the VM is
destroyed.  Because the source VM is "converted" to a non-SEV VM, KVM's
memory reclaim flows won't trigger cache maintenance, e.g. when all guest
memory is reclaimed in response to detaching from the mmu_notifier.

Note, relying on the destination VM to do cache maintenance isn't an option
as KVM doesn't require identical guest memory configurations, i.e. the
source VM may have access to memory that the destination VM does not.
Enforcing equivalent memory configurations is infeasible, as it would
require a *deep* comparison of memslots, e.g. to verify that not only are
the memslot identical, but what the memslots point at is also identical.

Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260923163721.1584779-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 209 insertions, 0 deletions

diff --git a/arch/arm/mm/pgd.c b/arch/arm/mm/pgd.c
new file mode 100644
index 000000000..447945836
--- /dev/null
+++ b/arch/arm/mm/pgd.c
@@ -0,0 +1,209 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/arch/arm/mm/pgd.c
+ *
+ *  Copyright (C) 1998-2005 Russell King
+ */
+#include <linux/mm.h>
+#include <linux/gfp.h>
+#include <linux/highmem.h>
+#include <linux/slab.h>
+
+#include <asm/cp15.h>
+#include <asm/pgalloc.h>
+#include <asm/page.h>
+#include <asm/tlbflush.h>
+
+#include "mm.h"
+
+#ifdef CONFIG_ARM_LPAE
+#define _pgd_alloc(mm)		kmalloc_objs(pgd_t, PTRS_PER_PGD, GFP_KERNEL | __GFP_ZERO)
+#define _pgd_free(mm, pgd)	kfree(pgd)
+#else
+#define _pgd_alloc(mm)		__pgd_alloc(mm, 2)
+#define _pgd_free(mm, pgd)	__pgd_free(mm, pgd)
+#endif
+
+/*
+ * need to get a 16k page for level 1
+ */
+pgd_t *pgd_alloc(struct mm_struct *mm)
+{
+	pgd_t *new_pgd, *init_pgd;
+	p4d_t *new_p4d, *init_p4d;
+	pud_t *new_pud, *init_pud;
+	pmd_t *new_pmd, *init_pmd;
+	pte_t *new_pte, *init_pte;
+
+	new_pgd = _pgd_alloc(mm);
+	if (!new_pgd)
+		goto no_pgd;
+
+	/*
+	 * Copy over the kernel and IO PGD entries
+	 */
+	init_pgd = pgd_offset_k(0);
+	memcpy(new_pgd + USER_PTRS_PER_PGD, init_pgd + USER_PTRS_PER_PGD,
+		       (PTRS_PER_PGD - USER_PTRS_PER_PGD) * sizeof(pgd_t));
+
+	clean_dcache_area(new_pgd, PTRS_PER_PGD * sizeof(pgd_t));
+
+#ifdef CONFIG_ARM_LPAE
+	/*
+	 * Allocate PMD table for modules and pkmap mappings.
+	 */
+	new_p4d = p4d_alloc(mm, new_pgd + pgd_index(MODULES_VADDR),
+			    MODULES_VADDR);
+	if (!new_p4d)
+		goto no_p4d;
+
+	new_pud = pud_alloc(mm, new_p4d, MODULES_VADDR);
+	if (!new_pud)
+		goto no_pud;
+
+	new_pmd = pmd_alloc(mm, new_pud, 0);
+	if (!new_pmd)
+		goto no_pmd;
+#ifdef CONFIG_KASAN
+	/*
+	 * Copy PMD table for KASAN shadow mappings.
+	 */
+	init_pgd = pgd_offset_k(TASK_SIZE);
+	init_p4d = p4d_offset(init_pgd, TASK_SIZE);
+	init_pud = pud_offset(init_p4d, TASK_SIZE);
+	init_pmd = pmd_offset(init_pud, TASK_SIZE);
+	new_pmd = pmd_offset(new_pud, TASK_SIZE);
+	memcpy(new_pmd, init_pmd,
+	       (pmd_index(MODULES_VADDR) - pmd_index(TASK_SIZE))
+	       * sizeof(pmd_t));
+	clean_dcache_area(new_pmd, PTRS_PER_PMD * sizeof(pmd_t));
+#endif /* CONFIG_KASAN */
+#endif /* CONFIG_LPAE */
+
+	if (!vectors_high()) {
+		/*
+		 * On ARM, first page must always be allocated since it
+		 * contains the machine vectors. The vectors are always high
+		 * with LPAE.
+		 */
+		new_p4d = p4d_alloc(mm, new_pgd, 0);
+		if (!new_p4d)
+			goto no_p4d;
+
+		new_pud = pud_alloc(mm, new_p4d, 0);
+		if (!new_pud)
+			goto no_pud;
+
+		new_pmd = pmd_alloc(mm, new_pud, 0);
+		if (!new_pmd)
+			goto no_pmd;
+
+		new_pte = pte_alloc_map(mm, new_pmd, 0);
+		if (!new_pte)
+			goto no_pte;
+
+#ifndef CONFIG_ARM_LPAE
+		/*
+		 * Modify the PTE pointer to have the correct domain.  This
+		 * needs to be the vectors domain to avoid the low vectors
+		 * being unmapped.
+		 */
+		pmd_val(*new_pmd) &= ~PMD_DOMAIN_MASK;
+		pmd_val(*new_pmd) |= PMD_DOMAIN(DOMAIN_VECTORS);
+#endif
+
+		init_p4d = p4d_offset(init_pgd, 0);
+		init_pud = pud_offset(init_p4d, 0);
+		init_pmd = pmd_offset(init_pud, 0);
+		init_pte = pte_offset_map(init_pmd, 0);
+		set_pte_ext(new_pte + 0, init_pte[0], 0);
+		set_pte_ext(new_pte + 1, init_pte[1], 0);
+		pte_unmap(init_pte);
+		pte_unmap(new_pte);
+	}
+
+	return new_pgd;
+
+no_pte:
+	pmd_free(mm, new_pmd);
+	mm_dec_nr_pmds(mm);
+no_pmd:
+	pud_free(mm, new_pud);
+no_pud:
+	p4d_free(mm, new_p4d);
+no_p4d:
+	_pgd_free(mm, new_pgd);
+no_pgd:
+	return NULL;
+}
+
+void pgd_free(struct mm_struct *mm, pgd_t *pgd_base)
+{
+	pgd_t *pgd;
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pgtable_t pte;
+
+	if (!pgd_base)
+		return;
+
+	pgd = pgd_base + pgd_index(0);
+	if (pgd_none_or_clear_bad(pgd))
+		goto no_pgd;
+
+	p4d = p4d_offset(pgd, 0);
+	if (p4d_none_or_clear_bad(p4d))
+		goto no_p4d;
+
+	pud = pud_offset(p4d, 0);
+	if (pud_none_or_clear_bad(pud))
+		goto no_pud;
+
+	pmd = pmd_offset(pud, 0);
+	if (pmd_none_or_clear_bad(pmd))
+		goto no_pmd;
+
+	pte = pmd_pgtable(*pmd);
+	pmd_clear(pmd);
+	pte_free(mm, pte);
+	mm_dec_nr_ptes(mm);
+no_pmd:
+	pud_clear(pud);
+	pmd_free(mm, pmd);
+	mm_dec_nr_pmds(mm);
+no_pud:
+	p4d_clear(p4d);
+	pud_free(mm, pud);
+no_p4d:
+	pgd_clear(pgd);
+	p4d_free(mm, p4d);
+no_pgd:
+#ifdef CONFIG_ARM_LPAE
+	/*
+	 * Free modules/pkmap or identity pmd tables.
+	 */
+	for (pgd = pgd_base; pgd < pgd_base + PTRS_PER_PGD; pgd++) {
+		if (pgd_none_or_clear_bad(pgd))
+			continue;
+		if (pgd_val(*pgd) & L_PGD_SWAPPER)
+			continue;
+		p4d = p4d_offset(pgd, 0);
+		if (p4d_none_or_clear_bad(p4d))
+			continue;
+		pud = pud_offset(p4d, 0);
+		if (pud_none_or_clear_bad(pud))
+			continue;
+		pmd = pmd_offset(pud, 0);
+		pud_clear(pud);
+		pmd_free(mm, pmd);
+		mm_dec_nr_pmds(mm);
+		p4d_clear(p4d);
+		pud_free(mm, pud);
+		mm_dec_nr_puds(mm);
+		pgd_clear(pgd);
+		p4d_free(mm, p4d);
+	}
+#endif
+	_pgd_free(mm, pgd_base);
+}